Inscribe triangle RST in the square with dimensions 4×4, as shown in the figure.
from the area of this square, 4*4=16, we remove the triangles with dimensions
3×4, 2×1 and 2×4, whose side lengths are shown in the figure, and we are left with the area of triangle RST.
so [tex]Area(RTS)=16- \frac{1}{2}*3*4- \frac{1}{2}*2*1- \frac{1}{2}*2*4=16-6-1-4=5[/tex] units squared
similarly,
[tex]Area(LMN)=4*3- \frac{1}{2}*1*4- \frac{1}{2}*2*2- \frac{1}{2}*2*3=12-2-2-3=5[/tex] units squared
Thus, the areas are equal.